Although dopamine is the primary regulator of prolactin release, endogenous opiate peptides are said to have important influences on the secretion of this hormone, which may differ between males and females. This R-15 grant proposes to investigate these issues in three specific Aims. 1) To examine prolactin secretion to met- or leu-enkephalin in males as well as females at different stages of the estrous cycle. 2) To repeat these studies in the presence of antagonists of specific opiate receptor subtypes. 3) To examine the effects of these same peptides on catecholamine secretion from dopaminergic neurons in the dissected hypothalamus.